Overrunning roller clutches typically have cage roller pockets with a pair of parallel side rails and flat base. A roller moves back and forth in the pocket, toward and away from the base, over a normal path of travel that does not bring the roller too near the pocket base. However, disturbing forces can occur that can cause one or more rollers to shift farther back toward the base of the pocket. Each roller is continually urged forwardly, away from it's pocket base, by an individual compression energizing spring. The most common type of energizing spring is a so called accordion spring, with a series of flat leaves joined at resilient folds or pleats to form a series of V's. The front and rear end spring leaves are passive, abutted with the roller and pocket base respectively. The intermediate, active spring leaves move together and apart about the live hinge of the pleats. The most critical part of such a spring is the pleat, which stores and releases energy. Ideally, the spring pleats would be protected again two possible kinds of damage. One potential risk is rubbing of the spring pleats against the pocket side rail inner surfaces as the spring compresses and expands with the moving roller. Another potential risk is over compression of the spring. Each pleat has a minimum thickness, beyond which it cannot be compressed without risking exceeding its elastic limit. Consequently, the spring as a whole has a characteristic solid height, the distance beyond which it cannot be compressed without risking stressing the pleats. The solid height corresponds roughly to the sum of the pleat minimum thicknesses on either side of the spring.
Recent patent activity has dealt with both aspects of accordion spring pleat protection. U.S. Pat. No. 4,368,809 to Husmann protects the spring pleats from side rail wear by with a tab on the front end pleat of the spring that rides between one side rail and an end of the roller, keeping the spring centered so that the pleats are spaced away from the side rails. U.S. Pat. No. 4,850,464 to Lederman provides a simpler spring which self protects its pleats against side rail wear without guidance from the roller. The type of accordion spring disclosed there, one in which all the pleats have the same subtended angle, also experiences an inherent side thrust toward one of the side rails as the spring expands and contracts. A deliberately lengthened rear end leaf of the spring hits one of the side rails as the spring shifts to the side, thereafter keeping all the pleats away from both side rails as the spring operates. U.S. Pat. No. 4,932,508 to Lederman deals with over compression. All leaves of the spring disclosed there, except for the front end leaf, have a special resilient finger lanced out of the center that is designed to hit and bend against an adjacent leaf only when high compression occurs, thereby providing a restoring force to prevent the spring from being compressed past its solid height. This design has limitations in that it works only through the resilience of the fingers, which inevitably require some space between the leaves, and so limits how far the spring can totally compress. It is also a more difficult design to manufacture, as compared to a simple spring with uninterrupted leaves. Also, the spring fingers per se do nothing to prevent rubbing wear of the spring pleats.